The production of optical multilayer systems, which are also referred to as interference layers, plays an important role in, for example, optical products such as band-pass filters, edge filters, cold mirrors, beam splitters, and antireflection coatings. The goal of such a coating is to achieve transmission or reflection at the multilayer system that is as complete as possible within a prescribed wavelength range but achieve negligible transmission or reflection in the wavelength ranges outside thereof, with the smallest transition region possible. Meeting these demands requires a large number of individual layers, wherein, for example, layers with high and low refractive index are alternately applied to the substrate; however, it is also possible for two layers with a high refractive index or two layers with a low refractive index to follow one another directly.
When producing such complex layer systems, more particularly when producing multilayers with specific functional properties, a regular measurement or check of the functional layers applied to the substrates is necessary in order to ensure the desired layer thicknesses and layer properties. To this end, use is made of test glasses, on which in each case a single layer is deposited and checked. In the case of complex optical filters, a plurality of test glass changes are required in order to achieve the filter specifications. In order to achieve the required accuracy, the test glass must be arranged on the site of the substrates and substantially experience the same coating as the substrate; furthermore the test glass change between the individual coating sequences should be as automated as possible, i.e. without manual replacement of the test glasses by an operator.
DE 36 04 624 A1 has disclosed a test glass changer that allows a test glass change when the coating chamber is sealed. A holder for holding a plurality of test glasses is mounted on a rotary disk, which is used to guide the substrates along a path through at least one coating material flow. The holder is moved with the rotary disk and is mounted such that it can rotate with respect to the rotary disk. An intermittent motion system, which is arranged along the path of the rotary disk, switches respectively one test glass into a position that is stationary with respect to the rotary disk, in which position said test glass, along with the substrates, is alternately guided through the beam path of the measurement device and the coating material flow for a prescribable number of revolutions of the rotary disk. The holder is covered by a cover, which is attached to the rotary disk in a stationary fashion and in each case only exposes a single test glass in its coating and measurement position. The holder is rotated by a moveable shift finger, which is arranged in the interior of the coating chamber and protrudes into the orbit of the rotary disk and interacts with projections on the holder. When the shift finger engages into a projection on the holder, a test glass is rotated out of its congruent position with the measurement window and the next test glass takes its place. Hence, the test glass changer in DE 36 04 624 A1 permits a test glass change with a sealed coating chamber. However, loading the test glass changer is very complicated because the individual test glasses must be inserted into the holder of the test glass changer through the substrate lock. Furthermore, the test glass changer shown in DE 36 04 624 A1 can only hold a comparatively small number (four) of test glasses, and so (at least) one manual replacement of the test glasses is necessary when producing a multilayer system.